Bip39 Passphrase. The seed phrase is often converted to the amount which is used as being the seed integer to a deterministic wallet that generates the many important pairs used in the wallet. For words that only have 3 letters, there's no 4th letter. For instance Using the word “incorporate”, https://yourtopdirectory.com/listings13101436/bip39-mnemonic-generator-https-linktr-ee-bip39-not-known-details-about-bip39-passphrase-generator